Control system for air-conditioning apparatus



Aug. 29, 1950 w. EWALD ETAL CONTROL 'syswm FOR AIR comnrrxoumc APPARATUS Filed June 19, 1948 hue/1501's wczlcl/ iller UZwfZesZ Patented Aug. 29, 1950 .1. GQNTROLSSTEM FOR'AIR CONDITIONING APPARATUS t-WarreitEwald'andUharies E. Miller-, Minne -rpolis,

' .-tion ing.fiqrporation,--1Viinneapolis, Minn, acorporation,of-Delaware can electrically-1actuatedavalve rthe liquid linel of the-refrigerating"zsystemzarid this valve in combina-tionrw with. azrzithermostatic expansion rvalve governsathelfiowi of -1efrigeraiit td the evaporator vamsua'lly inithe :form of. a. coil) bf. the s'ystem.

. FWhen-refrigerant isl admitted to the-evapoi ator,

can 'increaserin: pressure-occurs m the slictio'zi line therefor; whichinthrou'gh at pressure actuated r switch 5: causes 2 thetastartersl -for 'the 1 compressor motorandithe condensersm'otoreto start theni into toneif'ati'one: *andwtheyr run untilP the' s'dction line pressure is lower than lhat:at which the'said switchi isractuated: li 'sald motors iiiill -then stop when' the compressonand condenser -pumnaway ZDdICODdBIlSE therefrigerantfaster than i-t iseonertedrs into :gas ini the evaporator r.thermostatrcutsfibff'wthe supply o r-efrigerant' to ethe evaporator, :Tthe compressor: motor will con-- tinuet. in.;operation until. it reduces the s'uc'tion r-pressure: tozsthemsetting of the pressure actuated switch.

Ti'i'fIhissis: called the" fipump down or the system and the;compressor. mctor shonlw remain inac- "tive..zuntitmore:cooling isarequirediirt theispace to "138? cooled. .xHowever; rwhemethenvalve structure in tha compressor; becomes Worzrpsuction :pressnre deaks: zbackztherethrcugh tend tam rhbjedtiona-ble restarting of: the apparratus xaTIdKknfiWI-l as sho'rt cycling occurs, which is hard on the apparatus ..andr-increases current consumption.

zne-.ofstlre objectswof l the;presentt'in /eritioii 'is r tto providersimple, inexpensive? means. imapparaltus ofrthis :kind;"whicinpreyentsaahe short cycling' --action before mentionedawhenrz- SPaCElBUCuliIlgU-iS not -required.

Another object ofrstheeinyentionaistaitcipmvide in apparatusofethisakindgra simple, efieotive relay actuated. switch ring the circuitr ior. theipress-ure .actuated:.-switch-, which aielay; actuated: switoh sis zeontrolied .byirthei thermostat, sozthattzsaidt a clay aactuatedeswitchmasctietcipoweeovemmd contrhls 55- the pressure actuated -r-switch, whereby hshort cycling. operations are eliminated.

. l Theabove mentioned objects-- of theinyent-i-on,

as Well; as zothers,..together with the. advantages .Lthereot will more telly .appeani as the specification proceeds.

,. In the drawing; .the done .rfigurel .-thereof "is a f diagrammaticyiew illustrating the preferred-dorm j of .the. invention.

. Referring. now in cletaihto that embodiment of the invention. illnstratedin. the drawing, there is embcdiedfthereina refrigerant compressor-5 andlits driving. motor fi st condenser-'1 employing .water. as apart ofthe coolant. therefor'and which is circulated from a. tank a .by pump: 9. driven by a..motor1 i 51.1 The. evaporator .is.v indicated at "I l. andit is herein illustrated as;asernentine coil. "I'Its inlet end is connected by a conduit lZ-.t0.the "liquid receiver 13 preferably located in the water in the. tank 8. The outlet side off-the evaporator is connected. by a conduit l t with the. suction side .of the compressor 5 arid the pressure side of the 'compressor is connected bya conduit [5 leading toIthefloondenseri 3.. Air is blown through. the

evaporator by means 'offla blower -i ddrive'mby a "'motor 1?. Afterthe air has passed'through the evaporatorpwherein heat units. are extracted '-therefr-om,it is delivered with a sensible temperature and latentheat drop in thespace room to. be

cooled (not showmyandi in which islocated a temperature responsivetdevice1E8, suchas a, conventional thermostat.

' The motors 6; Wand I? arehereiirshown as of the three phasetype' and-'eachflhaS associated therewith a-moto1'-starter shown".only.diag1'am matically in the'drawing; "Such starters are Well known commercialproducts" and each" consists of amagnetth'at is energizedby a light current from the controls. "This magnetpulls into contact aheavy switclrwhich carries'currentto' the "associated-motor to be started. E'achs'tarter also includes a thermal overload protection device" so that contact for the heavy switch will" bebroken if --=too-much' current-passes to the associated "motor. ""The'starter'indicated at A is associated with the compressor motor 5 and is-conne'cted *thereto by-the conductors E9. Thastarter indicated at=-B is associ'ated with the motor I! for the blower l'fi' 'andis connected to said motor by thecozidnetofs 28$"The starter indicated at C is tassbo'iatdtvitli the motor Illwhich also'drives a blower (nofishowh) employed for blowing air through -the condenser and "this starter is conected'to said m'etor by "the conductors" 2 i several starter "SW; B and are connected-by conductors 22 to a source of operating current by means of a suitable fused disconnect switch indicated by the arrow heads 23. The parts thus far described are conventional in apparatus of this kind and no claim is made herein thereto.

In the conduit I2 is located a thermostatic expansion valve 24 and an electric solenoid con trolled valve 25. The valve 24 is actuated in response to the superheat of the evaporated refrigerant as it enters the suction side of the compressor by means of the conduit I l. To this conduit is attached a bulb 25 of temperature responsive fluid and this cylinder is connected by small diameter tubing 21 with the valve 24.

One side of the solenoid valve 25 is connected by a conductor 28 with one side of the space or room thermostat l8 and the other side of said valve is connected by a line 29 with one of the terminals of the motor starter B so as to receive energizin current therefrom when a lower temperature is called for in the space in which the thermostat i8 is located. This constitutes the main circuit for the apparatus so far as temperature control is concerned and when said circuit is open the apparatus remains passive or inoperative.

Conditions might arise wherein it is desired that the motor I 7 be energized to drive the blower to produce ventilation in the space in which the thermostat i8 is located. For this reason there is associated with said thermostat a toggle type of manually operable switch 3 that includes sets of contacts 3I32 and a double throw switch or control arms 3333. One of the contacts 32 is connected by a line 34 with the movable contact 35 of the thermostat. The set of contacts 32' is connected by a line 35 with a terminal in the motor starter B to receive current therefrom. The arms 33 of switch (it are connected by a line 3? with another terminal in the motor starter, to receive current therefrom.

When the apparatus is under the control of the thermostat E8, the switch arms 33 are thrown When it is L 39 and til with coacting terminals in the motor starter A. The means 38 also includes bellows ll and 42 that operate movable contacts and and these bellows are connected by tubing 25 and 46 with the pressure side and the suction side respectively of the compressor 5. The lines 3949 are connected to the movable contacts at and id and said contacts 43 and 44 move into and out of engagement with fixed contacts at the ends of a bridge 38a. When the movable contacts are engaged with the contacts at the ends of the bridge 38a, that part of the circuit including the line 39--40 is closed through the switch 38.

51 indicates a relay device which includes a contact 48 and a switch arm mmovable under the action of a relay coil 50. The contact dB is connected by a line 5! with the terminal 38a of the switch 38, while the movable contact 49 is connected by a conductor 52 with a terminal in they starter B. The coil 50 is connected by lines 4 5354 with the lines 28 and 29 leading to the solenoid valve 25.

The conductors I9, 20 and 2| constitute the power circuit for the motors 6, I! and while the conductors 28 and 29 constitute one part of the controlcircuit of the apparatus and the conductors 52, 53 and 54 form a second part of the control circuit and which includes the conductors 39 and 4!! respectively. The thermostat it through the conductors 28 and 29 controls the valve in the liquid refrigerant conduit l2 and this valve along with the valve 24 governs the flow of refrigerant to the evaporator.

When the thermostat l8 causes a flow of refrigerant to the evaporator, an increase in pressure occurs in the suction side of the compressor and such pressure causes the pressure actuated switch 38 to close the second part of the control circuit and energizes the starter A and C for the compressor motor 6 and condenser motor In and starts them into operation. When so started, these motors will continue to run until the suction pressure reduces to one that is lower than the setting for the pressure switch 38. The said motors will stop if the compressor and the condenser pump away and condenses the refrigerant faster than the evaporator H converts the liquid refrigerant into gas.

When the thermostat operates through the valve 25 to cut on the supply of refrigerant to the evaporator, the compressor will continue in operation until itreduces the suction pressure to the setting of the pressure switch 38 and this continuance of the compressor to run is called a pump down. After this pump down has occurred, the compressor motor 5 stops and remains in this position until more cooling is required in the space, in which the thermostat !8 is located. However, if the suction pressure arises, due to a leak back of gas through the compressor or from refrigerant evaporation from the coil to the switch 33, a restarting of the apparatus with its attendant annoyance and waste of current energy would occur if it were not for the relay switch 61 and which restarting is known as short cycling.

It is apparent that the relay switch l! through the conductors 53- 54 and 2829 is under the control of and actuated by the thermostat I 8 and this switch is closed only when the thermo- ;stat calls for cooling. Therefore, through this relay, the thermostat has veto power over the pressure switch 38 and said switch cannot function to permit the short cycling action because of increased suction pressure, when the thermostat IB is satisfied with the temperature conditions in the space in which it is located.

By means of the relay 41, which is a simple and relatively inexpensive device that requires no manual attention or operation, short cycling of the apparatus is prevented, with the attending inconvenience, annoyance and waste of current energy.

While in describing the invention we have referred in detail to the form and arrangement of the parts involved, the same is to be considered only in the illustrative sense and therefore we do not wish to be limited thereto except as may be specifically set forth in the appended claims.

We claim as our invention:

1. A short cycling prevention circuit for refrigeration apparatus of the kind described, which embodies therein a motor driven refrigerant compressor, an operating circuit for said motor, athermostatically controlled switch having open and closed positions and responsive to the temperature of the medium to be cooled, a pressure actuated switch having open and closed positions and operatively responsive to a relatively high pressure of refrigerant in the suction side of said apparatus to establish its closed position, said thermostatically controlled switch and said pressure actuated switch each forming a part of the control for the operating circuit for said motor, and a third switch in said circuit having open and closed positions and forming another part of the control for said circuit, through said pressure operated switch, said third switch being open and closed with said thermostatically controlled switch and when open preventing the closing of said circuit through said pressure operated switch and the short cycling operation of said motor in the closing of said pressure operated switch due to said relative,

high pressure of refrigerant in said suction side of the apparatus, and produced by a leaking back of the same to said last mentioned switch when said thermostatically controlled switch is in its open position.

2. A short cycling prevention circuit for refrigeration apparatus of the kind described, which embodies therein a motor driven refrigerant compressor, an operating circuit for said motor, a thermostatically controlled switch having open and closed positions and responsive to the temperature of the medium to be cooled, a pressure actuated switch having open and closed positions and operatively responsive to a relative high pressure of refrigerant in the suction side of said apparatus to establish its closed position, said thermostatically controlled switch. and said pressure actuated switch each forming a part ofthe control for the operating circuit for said motor, and a third switch in said circuit and having open and closed positions and forming another part of the control for said circuit and including a relay energized to close said circuit through said pressure actuated switch when said third switch and said thermostatically controlled switch are in their closed positions, said third switch automatically opening when said thermostatically controlled switch is open and operating to prevent the closing of said circuit, through said pressure operated switch and the short cycling operation of said motor in the closing of said pressure operated switch due to said relative high pressure of refrigerant in said suction side of the apparatus, and produced by a leaking back of the same to said pressure operated switch when said thermostatically controlled switch is in its open position.

WARREN CHARLES E. MILLER.

REFERENCES CITED Name Date N w on "Ta-m. 11

Number 2,342,728 

